Normally, a feed water pump control device installed in an office building or condominium is such that an estimated constant end pressure control, which controls water pressure at a demand end to a virtual constant by controlling a feed water pump discharge side pressure, is employed.
The estimated constant end pressure control can be employed without problem in a feed water pipe system wherein a water tank, or the like, is installed on the intake side of the feed water pump, and boost pressure changes little. However, in the kind of case wherein the feed water pump is connected directly part way along the feed water pipe, the boost pressure changes depending on the status of water use, meaning that, when controlling so that the feed water pump discharge side pressure is a constant end pressure, it may be difficult to supply an amount of water appropriate to the amount of water that should be fed.
When the head height (the discharge side pressure at a time of maximum quantity) in the feed water pump is clear, the boost pressure is detected by a pressure sensor installed on the intake side of the feed water pump, and by applying the boost pressure to an appropriate formula, it is possible to obtain simple linearized characteristics showing the relationship between the operating frequency of the feed water pump and the discharge side pressure. By controlling the operating frequency of the feed water pump in accordance with the simple linearized characteristics so that the discharge side pressure is such that the estimated end pressure is constant, an estimated constant end pressure control is theoretically possible.
According to the heretofore described method, although the discharge side pressure at a time of maximum quantity virtually coincides with the simple linearized characteristics, errors occur in the relationship between the quantity and discharge side pressure in a quantity range from zero until reaching a maximum value.
In particular, in an office building or condominium, it is very rare that the feed water pump is operated for a long time at maximum quantity, and normally it is often the case that operation is at half maximum quantity or less. Consequently, errors are likely to occur between the actual discharge side pressure of the feed water pump and the originally necessary discharge side pressure, as a result of which, there is a problem in that there is wasteful expenditure on electricity costs and water costs, which works against resource and energy saving.
Also, although it is also feasible to carry out an estimated constant end pressure control using two analog detection values, from a quantity sensor that detects the actual quantity and a discharge side pressure sensor, two sensors are necessary in this case.
Herein, as feed water pump control devices using an estimated constant end pressure control, those described in, for example, JP-A-5-133343 and JP-A-2001-123962 are publicly known.
The heretofore known technology according to JP-A-5-133343 includes an inverter device 106 and motor M for driving a pump P, pressure sensors 101 and 107 installed on the intake side and discharge side respectively of the pump P on a feed water pipe 200, pressure selection means 102, target pressure computing means 103, rotation speed control means 104, and rotation speed detection means 105, as shown in FIG. 5.
The heretofore known technology according to JP-A-5-133343 is such that the target pressure computing means 103 obtains a target pressure signal S3 in accordance with the rotation speed of the motor M using an intake side pressure signal S2X, and outputs the target pressure signal S3 to the rotation speed control means 104. A first setting pressure PA and a pressure signal PBX from the pressure selection means 102 are input into the target pressure computing means 103. The pressure selection means 102 outputs the larger of a second setting pressure PB, smaller than the first setting pressure PA, and the pressure signal S2X as the pressure signal PBX.
The rotation speed control means 104 controls the output frequency of the inverter device 106 so that the discharge side pressure signal S2 coincides with the target pressure signal S3, thereby operating the motor M.
According to the heretofore known technology, when the intake side pressure signal S2X exceeds the second setting pressure PB, it is possible to reduce the pump P discharge side pressure, even when the boost pressure is abnormally high, by substituting the setting pressure PB with the pressure signal S2X, and continuing operation.
Also, the heretofore known technology according to JP-A-2001-123962 includes pressure sensors 101 and 107 installed on the intake side and discharge side respectively of a pump P, a subtractor 108, maximum frequency computing means 109 and minimum frequency computing means 110, end target pressure computing means 111, moving average means 112, subtraction means 113 that obtains a deviation between a target pressure, which is the output of the moving average means 112, and a discharge side pressure detection value, proportional integral means 114, and addition means 115 that adds the output of the proportional integral means 114 and an actual inverter frequency fin, thereby obtaining a frequency command value of the inverter device 106, as shown in FIG. 6.
A maximum quantity Qmax is input into the maximum frequency computing means 109, while a maximum setting pressure Pmax, a minimum setting pressure Pmin, and the inverter frequency fin are input into the end target pressure computing means 111.
The heretofore known technology according to JP-A-2001-123962 is such that the maximum frequency computing means 109 and minimum frequency computing means 110 obtain a pressure difference ΔP between the discharge pressure and intake pressure of the pump P, and a maximum frequency fmax and minimum frequency fmin from the maximum quantity Qmax. Also, the end target pressure computing means 111, using the maximum frequency fmax, minimum frequency fmin, maximum setting pressure Pmax, minimum setting pressure Pmin, and inverter frequency fin, computes a target pressure P using a predetermined formula. Then, by the proportional integral means 114 adding a deviation between a moving average value of the target pressure P obtained by the moving average means 112 and a discharge side pressure detection value to the inverter frequency fin, using a proportional integral computation, a frequency command value of the inverter device 106 is computed.
As this heretofore known technology is such that the target pressure P is computed using the maximum frequency fmax and minimum frequency fmin, based on the pressure difference ΔP between the discharge pressure and intake pressure of the pump P, a highly accurate estimated constant end pressure control, unaffected by disturbance, is possible.